[InstSimplify] simplify power-of-2 (single bit set) sequences

As discussed in PR42314:
https://bugs.llvm.org/show_bug.cgi?id=42314

Improving the canonicalization for these patterns:
rL363956
...means we should adjust/enhance the related simplification.

https://rise4fun.com/Alive/w1cp

  Name: isPow2 or zero
  %x = and i32 %xx, 2048
  %a = add i32 %x, -1
  %r = and i32 %a, %x
  =>
  %r = i32 0

llvm-svn: 363997
This commit is contained in:
Sanjay Patel 2019-06-20 22:55:28 +00:00
parent 73986707bd
commit b342f026a4
2 changed files with 12 additions and 8 deletions

View File

@ -1845,6 +1845,16 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
return Op1;
}
// This is a similar pattern used for checking if a value is a power-of-2:
// (A - 1) & A --> 0 (if A is a power-of-2 or 0)
// A & (A - 1) --> 0 (if A is a power-of-2 or 0)
if (match(Op0, m_Add(m_Specific(Op1), m_AllOnes())) &&
isKnownToBeAPowerOfTwo(Op1, Q.DL, /*OrZero*/ true, 0, Q.AC, Q.CxtI, Q.DT))
return Constant::getNullValue(Op1->getType());
if (match(Op1, m_Add(m_Specific(Op0), m_AllOnes())) &&
isKnownToBeAPowerOfTwo(Op0, Q.DL, /*OrZero*/ true, 0, Q.AC, Q.CxtI, Q.DT))
return Constant::getNullValue(Op0->getType());
if (Value *V = simplifyAndOrOfCmps(Q, Op0, Op1, true))
return V;

View File

@ -93,10 +93,7 @@ define i64 @pow2b(i32 %x) {
define i32 @pow2_decrement(i32 %p) {
; CHECK-LABEL: @pow2_decrement(
; CHECK-NEXT: [[X:%.*]] = shl i32 1, [[P:%.*]]
; CHECK-NEXT: [[A:%.*]] = add i32 [[X]], -1
; CHECK-NEXT: [[R:%.*]] = and i32 [[A]], [[X]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: ret i32 0
;
%x = shl i32 1, %p
%a = add i32 %x, -1
@ -106,10 +103,7 @@ define i32 @pow2_decrement(i32 %p) {
define <2 x i32> @pow2_decrement_commute_vec(<2 x i32> %p) {
; CHECK-LABEL: @pow2_decrement_commute_vec(
; CHECK-NEXT: [[X:%.*]] = and <2 x i32> [[P:%.*]], <i32 2048, i32 2048>
; CHECK-NEXT: [[A:%.*]] = add <2 x i32> [[X]], <i32 -1, i32 -1>
; CHECK-NEXT: [[R:%.*]] = and <2 x i32> [[X]], [[A]]
; CHECK-NEXT: ret <2 x i32> [[R]]
; CHECK-NEXT: ret <2 x i32> zeroinitializer
;
%x = and <2 x i32> %p, <i32 2048, i32 2048>
%a = add <2 x i32> %x, <i32 -1, i32 -1>